Editing Digital Addressable Lighting Interface (section)

==Technical overview==
A DALI network consists of at least one application controller and bus power supply (which may be built into any of the products) as well as input devices (e.g. sensors and push-buttons), control gear (e.g., [[electrical ballast]]s, LED drivers and [[dimmer]]s) with DALI interfaces. Application controllers can control, configure or query each device by means of a bi-directional data exchange. Unlike [[DMX512|DMX]], multiple controllers can co-exist on the bus. The DALI protocol permits addressing devices individually, in groups or via broadcast.<ref>{{Cite web|url=https://www.digitalilluminationinterface.org/dali/|title = Standards - Digital Illumination Interface Alliance}}</ref>  Scenes can be stored in the devices, for recall on an individual, group or broadcast basis.  Groups and scenes are used to ensure simultaneous execution of level changes, since each packet requires about 25 ms - or 1.5 seconds if all 64 addresses were to change level.

Each device is assigned a unique short address between 0 and 63, making up to 64 devices possible in a basic system. Address assignment is performed over the bus using a "commissioning" protocol built into the DALI controller, usually after all hardware is installed, or successively as devices are added.   The Device Address is commonly a LED driver with one or many LEDs sharing the same level.   A DT6 driver is for single color temperature applications, a DT8 driver is used for CCT color tuning, or RGBWW multi color applications - for example a strip where all the "pixels" have the same color.

Data is transferred between devices by means of an asynchronous, half-duplex, serial protocol over a two-wire bus with a fixed data transfer rate of {{nowrap|1200 [[Bit rate|bit/s]]}}.  Collision detection is used to allow multiple transmitters on the bus.

A single pair of wires comprises the [[Bus (computing)|bus]] used for communication on a DALI network. The network can be arranged in bus or star [[network topology|topology]], or a combination of these.  Each device on a DALI network can be addressed individually, unlike DSI and 0–10V devices. Consequently, DALI networks typically use fewer wires than DSI or 0–10V systems.

The bus is used for both signal and bus power.  A power supply provides a current limited source of up to 250&nbsp;mA at typically 16&nbsp;V DC; each device may draw up to 2&nbsp;mA unless bus-powered.{{r|da|p=20,35}}  While many devices are mains-powered (line-powered), low-power devices such as motion detectors may be powered directly from the DALI bus.  Each device has a [[bridge rectifier]] on its input so it is polarity-insensitive.  The bus is a [[wired-AND]] configuration where signals are sent by briefly shorting the bus to a low voltage level.  (The power supply is required to tolerate this, limiting the current to 250&nbsp;mA.)

Although the DALI control cable operates at [[Extra-low voltage|ELV]] potential, it is not classified as [[SELV]] (''Safety'' Extra Low Voltage) and therefore should not be Accessible to the user. The requirements of the DALI standard IEC 62386-101 (clause 4.9.2) categorise the interface as [[Extra-low_voltage#Functional_extra-low_voltage_(FELV)|FELV]]. It also requires that the interface have at least Basic insulation from AC mains, and Supplementary insulation from the interface to any user Accessible part like the cover of the equipment. Clause 4.10 does not permit any part of the interface to be connected to Protective Earth unless this occurs at a low power (less than 250mA) bus power supply, or via a Class Y safety capacitor. This requirement for an unearthed interface precludes the use of an earthed conductor to meet the FELV requirements of IEC 60364-4-41 clause 411.7, further mandating the use of Basic insulation between AC mains and the interface. This also means that the interface cable is required to be mains-rated and permits it to be run next to mains cables or within a multi-core cable which includes mains power.

The network cable is required to provide a maximum drop of {{nowrap|2 volts}} along the cable.{{r|da|p=19}}  At 250&nbsp;mA of supply current, that requires a resistance of ≤&nbsp;{{val|4|u=Ω}} per wire.  The wire size needed to achieve this depends on the length of the bus, up to a recommended maximum of {{val|2.5|ul=mm2}} at 300&nbsp;m when using the maximum rating of bus power supply.

The speed is kept low so no [[Electrical termination|termination resistors]] are required,<ref name=da>{{cite web |url=http://www.dali-ag.org/c/manual_gb.pdf |title=Digital Addressable Lighting Interface |publisher=DALI AG, Activity Group, ZVEI-Division Luminaires |website=DALI |date=September 2001 |access-date=12 July 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130627012349/http://www.dali-ag.org/c/manual_gb.pdf |archive-date=27 June 2013 }}</ref>{{Rp|21}} and data is transmitted using relatively high voltages ({{val|0|4.5|u=V}} for low and {{val|16|6.5|u=V}} for high{{r|da|p=19}}) enabling reliable communications in the presence of significant electrical noise.  (This also allows plenty of headroom for a bridge rectifier in each slave.)

Each bit is sent using [[Differential Manchester encoding|Manchester encoding]] (a "1" bit is low for the first half of the bit time, and high for the second, while "0" is the reverse), so that power is present for half of each bit.  When the bus is idle, the voltage level is continuously high (which is not the same as a data bit).  Frames begin with a "1" [[start bit]], then 8 to 32 data bits with the most significant bit first (standard [[RS-232]] has the least significant bit first), followed by a minimum of 2.45&nbsp;ms of idle.